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[EDIT] FILE: threadlocal.py

# engine/threadlocal.py
# Copyright (C) 2005-2021 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""Provides a thread-local transactional wrapper around the root Engine class.

The ``threadlocal`` module is invoked when using the
``strategy="threadlocal"`` flag with :func:`~sqlalchemy.engine.create_engine`.
This module is semi-private and is invoked automatically when the threadlocal
engine strategy is used.
"""

import weakref

from . import base
from .. import util

class TLConnection(base.Connection):
    def __init__(self, *arg, **kw):
        super(TLConnection, self).__init__(*arg, **kw)
        self.__opencount = 0

def _increment_connect(self):
        self.__opencount += 1
        return self

def close(self):
        if self.__opencount == 1:
            base.Connection.close(self)
        self.__opencount -= 1

def _force_close(self):
        self.__opencount = 0
        base.Connection.close(self)

class TLEngine(base.Engine):
    """An Engine that includes support for thread-local managed
    transactions.

"""

_tl_connection_cls = TLConnection

@util.deprecated(
        "1.3",
        "The 'threadlocal' engine strategy is deprecated, and will be "
        "removed in a future release.  The strategy is no longer relevant "
        "to modern usage patterns (including that of the ORM "
        ":class:`.Session` object) which make use of a "
        ":class:`_engine.Connection` "
        "object in order to invoke statements.",
    )
    def __init__(self, *args, **kwargs):
        super(TLEngine, self).__init__(*args, **kwargs)
        self._connections = util.threading.local()

def contextual_connect(self, **kw):
        return self._contextual_connect(**kw)

def _contextual_connect(self, **kw):
        if not hasattr(self._connections, "conn"):
            connection = None
        else:
            connection = self._connections.conn()

if connection is None or connection.closed:
            # guards against pool-level reapers, if desired.
            # or not connection.connection.is_valid:
            connection = self._tl_connection_cls(
                self,
                self._wrap_pool_connect(self.pool.connect, connection),
                **kw
            )
            self._connections.conn = weakref.ref(connection)

return connection._increment_connect()

def begin_twophase(self, xid=None):
        if not hasattr(self._connections, "trans"):
            self._connections.trans = []
        self._connections.trans.append(
            self._contextual_connect().begin_twophase(xid=xid)
        )
        return self

def begin_nested(self):
        if not hasattr(self._connections, "trans"):
            self._connections.trans = []
        self._connections.trans.append(
            self._contextual_connect().begin_nested()
        )
        return self

def begin(self):
        if not hasattr(self._connections, "trans"):
            self._connections.trans = []
        self._connections.trans.append(self._contextual_connect().begin())
        return self

def __enter__(self):
        return self

def __exit__(self, type_, value, traceback):
        if type_ is None:
            self.commit()
        else:
            self.rollback()

def prepare(self):
        if (
            not hasattr(self._connections, "trans")
            or not self._connections.trans
        ):
            return
        self._connections.trans[-1].prepare()

def commit(self):
        if (
            not hasattr(self._connections, "trans")
            or not self._connections.trans
        ):
            return
        trans = self._connections.trans.pop(-1)
        trans.commit()

def rollback(self):
        if (
            not hasattr(self._connections, "trans")
            or not self._connections.trans
        ):
            return
        trans = self._connections.trans.pop(-1)
        trans.rollback()

def dispose(self):
        self._connections = util.threading.local()
        super(TLEngine, self).dispose()

@property
    def closed(self):
        return (
            not hasattr(self._connections, "conn")
            or self._connections.conn() is None
            or self._connections.conn().closed
        )

def close(self):
        if not self.closed:
            self._contextual_connect().close()
            connection = self._connections.conn()
            connection._force_close()
            del self._connections.conn
            self._connections.trans = []

def __repr__(self):
        return "TLEngine(%r)" % self.url

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